Snap action switch



' Dec 4, 1956 B. IMMEL 2,773,145

SNAP ACTION swrrcu Filed July I9, 1954 WITNESSES. I V INVENITOR 54% Ralph B.Immel. 27%

FMCigJW ATTORNEY United States Patent SNAP ACTION SWITCH Ralph B. Immel, Williamsville, N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 19, 1954, Serial No. 443,997

7 Claims. (Cl. 20067) This invention relates, generally, to electric switches and more in particular to that class of switches known in the art as snap switches.

The precision control of automatic machinery often requires many limit switches and small control devices. For industrial control applications, a snap switch that is rugged, dependable and operates continually at precisely the same point of operating plunger travel, is preferred to one that may operate on an extremely small movement or force. Snap switches falling in this general category can be used as a contact mechanism in limit switches or relays. It is to this general type of switch device that this invention is particularly directed.

One object of this invention is to provide a snap switch which is simple with respect to operational requirements and positive in operation.

Another object of this invention is to provide a snap action switch which is easily manufactured and assembled.

A further object of this invention is to provide a snap action switch which is rugged and has a long life expectancy in rated service.

Still another object of this invention is to provide a snap action switch which is fabricated from stamped and shaped light weight spring sheet metal parts.

The foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will become apparent from a study of the following specification when considered in conjunction with the accompanying drawings, in which:

Figure 1 is an assembled top view of a snap action type of switch embodying the principles of this invention;

, Fig. 2 is an elevational view of the switch shown in Fig. 1 with the front cover removed showing the switch mechanism;

Fig. 3 is a view similar to Fig. 2 but showing the switch mechanism in a second position;

Fig. 4 is a detail of the movable contact bridge embodied in the switch assembly of the preceding figures; and

Fig. 5 is an exploded perspective view of the switch mechanism.

The switch arrangement is a simply constructed assembly embodying a two-piece molded housing comprising a base I and a front cover 2. This housing may be formed of any suitable electric insulating material, one suitable class being the phenolic resins commonly used for such applications. As seen in Figs. 2 and 3, the base 1 supports two pairs of stationary contacts respectively designated 4 and 6. The respective contacts of the separate pairs are arranged in side-by-side relationship and are provided with suitable studs 4a, for example, as seen in Fig. 5, which may be molded in or pressfitted into suitable cavities in the base topositivelylocate and support the stationary contacts. The corresponding contacts of the respective pairs are positioned in spaced confronting relationship, one above the other, so that ice the respective contact buttons 4b and 6b are in coaxial relationship.

As will be seen by reference to Figs. 2 and 3, a movable contact bridge, generally designated 8, is disposed between the confronting stationary contacts. This bridge is fabricated of a single piece of light-weight electrical conducting spring sheet material such as beryllium cop-- per. The manufacture of the contact bridge involves a single stamping operation and simple bending opera-- tions to produce the part of the configuration shown. The movable contact bridge comprises a pair of con-- tact platforms 1t] spaced longitudinally from each other a distance corresponding to the spacing of the contacts of the respective pairs of stationary contacts, and eaclr platform is equipped with a contact assembly 12 on its upper and lower faces. These contacts, as well as the stationary contacts 4b and 6b, may be secured to their respective mounts in any suitable manner, for example, by riveting, brazing or welding. These contacts arepreferably of the dome-shape variety. The side edges of the respective contact platforms of the movable contact bridge are joined by means of the integral fiat spring members 14 which are bent downwardly from the plane surfaces of the contact platforms as best seen in Fig. 5, such that the width dimension of these spring members 14 lie in positions approximately at right angles to the plane of the contact platforms to provide maximum stiffness in the direction of force transmission for contact engagement. The respective contact platforms are pro vided with bearing plates 16 at their inner confronting edges which are bent downwardly from the plane surface of the contact platforms. These are provided with substantially centrally located slots or openings 18 adapted to receive the extensions 20 at the extremities of a flat actuating spring 22 which, as seen in Figs. 2 and 3, is bowed between the respective bearing plates 16. The compressional force due to bowing of the fiat actuating spring 22 tensions the spring members 14 of the movable contact bridge which, in their position of normal tensioning as just described, occupy the position shown in dot-dash outline at 14a in Fig. 4.

A plunger assembly, generally designated 24, comprising a push button section 26, a stem 28 and a platform 30, is slidably mounted for vertical movement, as seen in Figs. 2 and 3, in suitable slots in the base 1. A channel-shaped moving contact guide 32, which is formed of sheet material, is received and secured in the bottom channel-shaped portion 33 of the platform 30 of the plunger. The moving contact guide 32 is provided with a coined pivot 34 which is adapted to receive the upper face of the actuating spring 22 which fits within. the channel sides of the moving contact guide. Both the moving contact guide 32 and the actuating spring 22. are provided with rectangular openings, respectively designated 36 and 33, adapted to clear the stem 28 of plunger 24.

In assembled position as seen by reference to Fig. 2, the moving contact bridge is carried by the plunger between positions engaging the lower set 4 or upper set 6 of stationary contacts. When as shown in Fig. 2 the movable contact bridge bridges the lower pair of stationary contacts 4, and the plunger 24 is depressed, the actuating spring 22 tends to straighten out which further tensions the springs 14 of the movable contact bridge, elongating the bridge assembly. This elongation provides a slight wiping action of the movable contacts across the faces of the respective stationary contacts to provide positive electrical connection therebetween. As the plungeris pressed downwardly against the'compression force of return spring 40, the actuating spring 22 straightens out and then begins to bow in the opposite direction. The oppositely acting forces of the actuating spring 22 in corn pression, and the springs 14 of the movable contact bridge in tension, results in a vertical component of force acting on the movable contact bridge which increases with the displacement of the actuating spring 22. Thus, at the instant this force is sufiicient to start the movable contact bridge moving upwardly, the force increases appreciably separating the movable bridge contacts from the lower pair of stationary contacts in a very abrupt manner and positively driving the movable contacts into wiping engagement with the upper pair of stationary contacts.

For switches of low voltage and current rating, this slight wiping action which is achieved is highly desirable in assuring good electrical contact engagement by displacing foreign particles from positions between the contacting faces due to the relative lateral displacement between the contact faces. In the absence of such wiping action, these foreign particles will result in arcing and contact heating in varying degrees resulting in surface damage to the contacts considerably in excess of the wear resulting from the light wiping action described.

When the plunger 24 is released from the position illustrated in Fig. 3. return spring 40 drives the plunger back to the position illustrated in Fig. 2, and, consequently, snaps the switch back to the position therein illustrated.

It will be appreciated that the stationary contacts can be arranged so that the terminals are accessible at the ends, the bottom, the top or the front of the switch housing, the latter arrangement being shown herein.

With the proper selection of material thicknesses for the spring 22 and the movable contact bridge 8, the mech anism will require very little force for a positive snap action, and yet due to the orientation of the plane of the springs 14, is relatively very stiff in the direction of operation of the plunger. A switch of this design, it will be noted, can be made very shallow, as the moving contact member is quite narrow with respect to its length.

As a general proposition for optimum life from silver or silver alloy contacts, it is desirable to reduce the contact slide and wipe to a minimum. However, when a switch of this type is used on very low voltages, particularly below the contact arcing voltages mentioned above, an arrangement which does not provide contact wipe is a distinct disadvantage. At these low voltages, there may be insufficient voltage to break down the oxide film, and, hence, satisfactory electrical connection through the contacts will not be provided.

Although but one embodiment of this invention has been herein illustrated and described, it will be appreciated by those skilled in the art that numerous changes of this arrangement, both in its details and in the organization of such details, may be made without departing from the spirit and scope hereof. Accordingly, it is intended that the foregoing disclosure and the showings made in the drawing shall be considered only as illustrative of the principles of this invention and not interpreted in a limiting sense.

I claim as my invention:

1. A two position snap switch comprising two pairs of stationary contacts, electrical insulating means mounting the corresponding contacts of the respective pairs in spaced confronting relation, a movable contact bridge of electrical conducting spring metal having a pair of spaced contact platforms interconnected by a pair of fiat oppositely bowed spring members the planes of which are substantially at right angles to the planes of the contact platforms, contacts mounted on said platforms, a flat actuating spring member bowed in a first position between the confronting edges of said platforms exerting forces thereon in opposition to those of said oppositely bowed flat spring members, a plunger slidably mounted in said electrical insulating means, and means on said plunger engaging said flat actuating spring member and positioningsaid-rnovable contacts against one pair of said stationary contacts, movements of-said plunger in a direc tion to reversely bow said actuating spring member from all) said first position causing said actuating spring member to move said movable contacts away from each other against the tension of said oppositely bowed fiat spring members, reverse bowing of said actuating spring memher being effective to drive said movable contact bridge in a direction to engage the contacts thereon with the remaining pair of stationary contacts.

2. A two position snap switch comprising two pairs of stationary contacts, electrical insulating means mounting the corresponding contacts ofthe respective pairs in spaced confronting relation, a movable contact bridge of electrical conducting spring metal having a pair of spaced contact platforms interconnected by a pair of flat oppositely bowed spring members the planes of which spring members are substantially at right angles to the planes of said contact platforms, contacts mounted on said platforms, a flat actuating spring member bowedin a first position between the confronting edges of said platforms exerting forces thereon in opposition to those of said oppositely bowed flat spring members, a plunger slidably mounted in said electrical insulating means, and means on said plunger engaging said fiat actuating spring member and positioning said movable contacts against one pair of said stationary contacts, movement of said plunger in a direction to reversely bow said actuating spring member from said first position causing said actuating spring member to move said movable contacts away from each other against the tension of said oppositely bowed flat spring members, reverse bowing of said actuating spring member being effective to drive said movable contact bridge in a direction to engage the contacts thereon with the remaining pair of stationary contacts, and spring means engaging said plunger and biasing said plunger to a given axial position.

3. A. snap acting switch comprising a pair of spaced stationary contacts, a movable contact bridge including a pair of contact platforms and oppositely bowed strip spring members connected to corresponding sides of said platforms forming a bridge member which is resilient longitudinally of said oppositely bowed strip spring members, the planes of said strip spring members being disposed substantially at right angles to the planes of said contact platforms, a contact mounted on each platform, an actuating spring member bowed between the confronting edges of said platform, plunger means supporting said movable contact bridge in operative relation relative to said stationary contacts. and having a portion thereon adapted for engagement with said actuating spring memher for bowing said actuating spring member in opposite directions with respect to said movable contact bridge member and effecting snap-operation of the movable con tacts on said movable contact bridge member into and out of engagement with said stationary contacts.

4. A snap acting switch comprising a pair of spaced stationary contacts, a movable contact bridge including a pair of contact platforms and oppositely bowed strip spring members connected to corresponding sides of said platforms forming a bridge member which is resilient.

longitudinally ofsaid oppositely bowed strip spring members, the planes of said strip spring members beingdis posed substantially at right angles to the planes of said contact platforms, a contact mounted on each platform, an actuating spring member bowed between the. confronting edgesof said platform, plunger means support ingsaidmovable contact bridge in operative relation relative to said stationary contacts and having a portion thereon adapted for engagement with said actuating spring member for bowing said actuating spring member in opposite directions with respect to said movable contact bridge member and effecting snap operation of the movable contacts on said movable contact bridge member into and out of engagementwith said stationary contacts, and spring-means biasing said. plunger to. a given axial position.

5. A snap acting switch comprising a pair ofispaced stationary contacts, a movable contact bridge including a pair of contact platforms and oppositely bowed strip spring members connected to corresponding sides of said platforms forming a bridge member which is resilient longitudinally of said oppositely bowed strip spring members, the planes of said strip spring members being disposed substantially at right angles to the planes of said contact platforms, a contact mounted on each platform, an actuating spring member bowed between the confront ing edges of said platform, plunger means having a shoulder thereon engaging said actuating spring member for bowing said actuating spring member in opposite directions with respect to said movable contact bridge member and effecting snap operation of the movable contacts on said movable contact bridge member into and out of engagement with said stationary contacts, and a compression spring disposed about said plunger means biasing said actuating spring member against said shoulder and biasing said plunger means to a given position.

6. A snap acting switch comprising, an insulating support, a pair of spaced stationary contacts mounted on said insulating support, a plunger slidably mounted on said insulating support between said stationary contacts, a movable contact bridge comprising a pair of spaced contact platforms, flat springs interconnecting said platforms and having their width dimension disposed substantially at right angles to the plane of said contact platforms, contacts mounted on said contact platforms, said flat leaf springs being bowed in opposite directions and providing for displacement of said platforms towards and away from each other, an elongated spring member bowed between the inner edges of said contact platforms and tensioning said oppositely bowed fiat leaf springs, means securing said elongated spring member to said plunger with the contacts on said platforms disposed to engage and disengage said stationary contacts by movement of said plunger, movement of said plunger deflecting said elongated spring member between bowed positions on opposite sides of said movable contact bridge snapping said movable contact bridge between positions engaging and disengaging said stationary contacts.

7. A snap acting switch comprising, an insulating support, a pair of spaced stationary contacts mounted on said insulating support, a plunger slidably mounted on said insulating support between said stationary contacts, a movable contact bridge comprising a pair of spaced contact platforms, fiat springs interconnecting said platforms and having their width dimension disposed substantially at right angles to the plane of said contact platforms, contacts mounted on said contact platforms, said flat leaf springs being bowed in opposite directions and providing for displacement of said platforms towards and away from each other, an elongated spring member bowed between the inner edges of said contact platforms and tensioning said oppositely bowed fiat leaf springs, means securing said elongated spring member to said plunger with the contacts on said platforms disposed to engage and disengage said stationary contacts by movement of said plunger, movement of said plunger deflecting said elongated spring member between bowed positions on opposite sides of said movable contact bridge snapping said movable contact bridge between positions engaging and disengaging said stationary contacts, and spring means biasing said plunger to a given position.

References Cited in the file of this patent UNITED STATES PATENTS 2,267,164 Newton Dec. 23, 1941 2,400,754 Hausler May 12, 1946 2,466,459 MacFarland Apr. 5, 1949 2,512,306 Clark et al June 20, 1950 2,518,255 Roeser Aug. 8, 1950 

